Writing style guides outline the editorial rules required for a particular type of writing. They might be about simple things like grammar and punctuation, or they might be more substantive questions about citation, layout, or format. Some guides also speak to voice.
It's generally advisable to check with a publication or publisher to determine which guide they follow.
Associated Press (AP Style)
Associated Press is the go-to guide for journalists and news writing. It has special sections dedicated to areas of interest such as fashion, food, and sports. AP Style sometimes covers magazine content as well.
It was originally written with the news wire in mind, so symbols and extras like italics and underlining are kept to a minimum. Latin names are printed without their accents in straight AP Style, although many publications correct this in their house styles.
AP Style is updated every spring, so keeping up with its current rules can admittedly be a challenge, but you can usually find updates online
Chicago Manual of Style (CMS)
CMS is the standard for book publishing, both fiction and non-fiction. It's not generally used for scholarly publishing such as journals and research, but it might be used for history.
CMS issued its 17th edition in 2017. Be warned—it's extremely comprehensive, a big, multi-paged guide.
Modern Language Association (MLA)
The Modern Language Association style is almost exclusively used in the academic world. It applies mostly to literature and humanities.
This is likely the style first introduced to most writing students and undergrads. It does carry some similarities to CMS teachings, although it's more focused on citation and documentation.
American Psychological Association (APA)
The APA carries its own standard for the social sciences, such as psychology, sociology, education, and politics. APA style is sometimes used for engineering and business work as well.
Turabian style is named after the book’s author, Kate Turabian. It focuses on research work and is used for the academic arm of many subjects. In fact, many grad and undergrad students are directed to use Turabian despite the availability of another system in their discipline.
The CMS actually refers students to Turabian, and many will find it much easier to navigate.
Alternative Style Guides
- AMA: The American Medical Association style guide is in its 10th edition as of 2019. It's published by Oxford Press. Except for a few special cases, this is the go-to manual for health, medicine, and biology subjects.
- NLM: The National Library of Medicine has an online-only style guide that's often used in some of the AMA disciplines.
- CSE: The Council of Science Editors Manual covers natural sciences and biology.
- ACS: The American Chemical Society got in on the act with a style guide specifically for chemists. Chances are that you already know about this guide if you write about chemistry, but an ACS-style crib sheet is available if you ever need it.
- ASA: The American Sociological Association has a guide similar to that of APA, although the APA still seems to be more popular, even with more sociological-oriented disciplines.
- Bluebook: Bluebook citation is used in the legal profession.
- Harvard Style: Also called the Author-Date style of citation, this isn't actually a fully published guide, but it can be useful with regard to referencing.
Chances are you'll find any guidance you need as a freelance writer in one or more of these guides.